Leak in Garage

Hello! This is my first question, I hope a state this problem so you can understand. I purchased a home 9 months ago, and I have a unfinished garage. The garage is 2 car, no insulation, finished ceiling(room above garage) and two wall, one wall dining room, and the other finished wall a sm laundry room behind it. There is a door in the garage(with finished wall), that leads to the laundry room and goes to kitchen. Ok, so finally here is the proplem, I noticed that in one corner of the garage(the part that is attached to the house), there is a small leak that comes from the ceiling and sm staining on the plywood. The leak is very small and this corner gets slighly damp with large rain, and rarely water accumulation on the garage floor. There is no water staining noted on the adjacent finished wall, and no drainage in the laundry room behind the finished wall. One thing I noticed is that the water staining in the garage corner is localized to an area where the wood siding nails are, actually the builder missed the stud and there are siding nails that are visiable all the way up the wall to the garage ceiling. Also during a heavy rain, I can hear a contstant steady drip sound. Do you think my problem is comming from the poorly placed siding nails, or possible, flashing problem where the garage meets the house. The leak is so insignificant at this time, I was planning on insulating the garage, and placing osb, is this leak going to cause a problem? Thanks.